1. Field of the Invention
This invention relates generally to the field of optical devices, and more specifically to an apparatus and method for modulation, switching and dynamic control of light transmission using photonic crystals.
2. Description of the Related Art
On-chip optical modulators have paramount significance as inter- and intra-chip optical interconnects become an essential solution to the great challenges in speed, power dissipation and electromagnetic interference (EMI) that modern very large scale circuitry (VLSI) technology is facing. On-chip optical modulators, especially monolithically integrated silicon modulators, coupled with external infrared lasers and silicon photonic waveguides, can transmit ultra-high bit rate (>10 Gbit/sec) signals with low loss and low cross talk. However, conventional telecom optical modulators using LiNbO3 or III-V semiconductor materials cannot be integrated on silicon substrates. Recently, Liu et al. demonstrated a silicon Mach-Zenhder interferometer (MZI) modulator (A. Liu, R. Jones, L. Liao, D. Samara-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, M. Paniccia, “A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor,” Nature, 427, 615-618, 2004) with 10 Gbit/sec speed. But the total device length is over 1 cm and is not suitable for on-chip optical interconnects. M. Lipson's group at Cornell University reported ultra-compact silicon ring-resonator modulators with 10 μm diameter (M. Lipson, “Compact electro-optic modulators on a silicon chip,” IEEE J. Sel. Topics in Quantum Electron., 12, 6, 1520-1526, 2006). However, a ring resonator is a narrow band (<0.1 nm) device, which cannot operate at very high speed (>10 Gbit/sec).
Photonic crystals are a class of novel materials that offer new opportunities for the control and manipulation of light. Essentially, a photonic crystal consists of a periodic lattice of dielectric materials. The underlying concept of photonic crystals originated from seminal work by Eli Yablonivitch and Sajeev John in 1987. The basic idea was to engineer a dielectric super-lattice so that it manipulates the properties of photons in essentially the same way that regular crystals affect the properties of electrons therein. Like the token of semiconductors, a photonic band gap exists for photons in a photonic crystal in a continuous range of frequencies where light is forbidden to travel regardless of its direction of propagation. Silicon photonic crystal modulators have been proposed and demonstrated based on MZI structures with length reduced by slow photon effect. For example, an 80 μm active length MZI modulator was demonstrated with 1 Gbit/sec electro-optic modulation (Y. Jiang, et al, “80-micron interaction length silicon photonic crystal waveguide modulator, Applied Physics Letter, vol. 87, No. 22, 2005). However, the total device length is still several millimeters when including the conventional splitting and merging waveguide. Although an all-photonic-crystal approach can further reduce the total length, such a device is very lossy, especially in the slow photon region. This kind of all-photonic-crystal modulator has never been realized.
Generally, on-chip and chip-to-chip optical interconnects desire an ultra-compact electro-optic modulator that can be monolithically integrated on silicon substrates. Also, it requires the modulator to operate at a high modulation speed (>10 Gbit/sec) with low power dissipation. Additionally, the modulator should cover an acceptable optical bandwidth (>1 nm) for stable performance and channel spacing. Electro-optic modulators based on new modulation mechanisms and new architectures are needed. An optical modulator satisfying all the aforementioned requirements does not exist until this moment.